Beryllium hydride compounds

ABSTRACT

1. THE PROCESS OF FORMING BERYLLIUM HYDRIDE COMPOUNDS ACCORDING TO THE REACTION OF BE(BH4)2 WITH AIRR&#39;&#39;R&#34; WHEREIN, R, R&#39;&#39; AND R&#34; ARE SELECTED FROM THE CLASS CONSISTING OF H AND ALKYL RADICALS OF 1 TO 8 CARBON ATOMS AND WHERIN AT LEAST ONE OF SAID R&#39;&#39;S IS AN ALKYL GROUP. 4. (BEH2)N(BH3)2 WHEREIN N VARIES FROM 3 TO 100.

United States Patent Clitt Y. Fnjikawa,'Los Angeles, Calif;, assignorsto" North American Rockwell Corporation No Drawing. Filed May 12, 1965,Ser. No. 455,676

Int. Cl. C01!) 6/24 US. Cl. 23-361 4 Claims This invention relates toenergetic compounds and a method of making same. More specifically, theinvention relates to a new reaction to form new beryllium-containingcompounds.

It is well known that beryllium is of great interest as a propellantfuel component since it is an extremely energetic element and serves toincrease the performance of the fuels. Usually, the beryllium iscombined with H in the form of beryllium hydride. The berylliumcompounds can be incorporated into solid propellant formulations or usedin liquid propellant applications.

Thus, an object of this invention is to provide a novel reaction whereinberyllium compounds useful particularly in propellant applications canbe formed from the same basic reaction through the variance of theproportion of reactants.

The above and other objects of the invention are accomplished by thereaction of beryllium borohydride, Be(BH with an alkyl aluminumcompound, AlRR'R", wherein R, R and R" are selected from a classconsisting of H and alkyl radicals of l to 8 C atoms and wherein atleast one of the Rs is an alkyl group. The reaction of the two compoundsis generally carried out in the presence of a conventional hydrocarbonsolvent at from about 0 to 100 C. Particularly good yields have beenobtained a at reaction temperatures of 60 to 65 C. When the reactantsare present in equal molar quantities the reaction proceeds according tothe following equation:

The byproduct compound remaining dissolved in the solvent has not beenseparated for characterization but is predicted to be AIB RRRH The (BeHformed is a solid. The alkyl aluminum compounds include, for example,methyl aluminum dihydride, butyl aluminum dihydride, dipropyl aluminumhydride, trioctyl aluminum and the like.

When an excess of alkyl aluminum compound is utilized, the reactionproceeds as follows:

( Solvent heat vacuum (BeHz); BRRR"T The initial precipitate of (BeH-BRRR" contains (BeH in amounts corresponding to 60 to 80 weight percent(BeH purity. The compound Al B (RR'R") is merely predicted and has notbeen defined. The additional heating in vacuo drives off the alkyl boroncompound, BRR'R", leaving (BeH of 90 to 97 weight perice cent purity.The ratio of AlRR'R" to Be(BH can vary from over 1:1 to 3:1. Thecompound (BeH is essentially the same as produced from reaction (I),(BeH is a polymeric type compound having the structure where x is anunknown which serves to indicate the polymeric nature of the compound.

Where an excess of Be(BH is utilized in a reaction, the compound (BeH(BH where n can vary from 3 to 100, is formed according to the followingreaction equation:

The product is a solid having a calculated high impulse. Following willbe a more detailed description of the three major reactions varying therelative relationships of the two reactive components utilized to formeither (a) (BeH or (b) (Bel-I (BH which are the desired end products.

Prior to the invention, solid beryllium hydride had been formedaccording to the following reaction:

The beryllium hydride formed is thermally stable at ambient pressure toapproximately 200 C. This form of beryllium hydride was not reactive toair, H O, B H Be(BH and Be(CH The (Bel-I formed from reaction (2) inaccord with this invention is generally about weight percent pure whenit first precipitates from the reaction with the major impurity beingboron alkyl, BRRR". As indicated, the precipitate is generally heated invacuo which drives oti the BRRR" to give a 97 weight percent BeH TheBel-I produced from both reactions (1) and (2) appears to beconsiderably different in its behavior than that resulting from thereaction of prior art as indicated above. The BeH of this invention issensitive to air and moisture indicating a high degree of reactivity.For example, the BeH reacts with B H in accord with the followingreaction to form a new compound hydroberyllium borohydride:

203cm)x B2110 (HBeBHr):

Additionally, the beryllium hydride of this invention reacts with Be(BHto form hydroberyllium borohydride. Neither of the above two reactionsto form hydroberyllium borohydride transpires with the BeH formed in theprior art. The compound (HBeBHQ was indicated previously but did nothave the same properties nor was it prepared in the same manner as the(HBeBH formed in Equation 5. Thus it can be seen that a new form ofberyllium hydride having different physical properties from thatpresently existing in the prior art has resulted from the novel reactionof this invention.

( QJ QZ One of the most interesting products formed from the basicreaction of the invention is that resulting from Equation 3 wherein theproduct (BeH (BH is formed. In order to obtain this product, an excessof Be(BH is utilized. The product formed is a polymerictype compoundhaving the following structural configuration:

where n, as previously noted, is a whole integer from 3 to 100. It isnoted that the BeH repeats itself in the chain with the EH used as achain terminator at each end. It hasbeen found that the higher the ratioof Be(BH4)2 to the AlRR'R" the shorter the chain obtained. The compoundformed will be referred to as a borane-terminated beryllium hydride. Itis a white non-volatile solid. The value of n or length of the polymeris determined by the solvent and ratios of Be(BH to AlRRR". Aromaticsolvents such as benzene give a higher n value than aliphatics. Otherexamples of solvents include cyclohexane, isopentane, ethane,hexadecane, mineral oil, toluene and the like. Additionally, the moreBe(BH present, the shorter the chains or lower the 11 value. Theborane-terminated beryllium hydride formed is inert to air, atmosphericmoisture, and Water at room temperature. It possesses good thermalstability which is indicated by no loss of hydrogen after being heatedfor two hours at 150 C. in a vacuum.

The borane terminated beryllium hydrides of the invention possessadvantages for utilization as a rocket fuel over the previously utilizedberyllium hydride. It is well known that impulse of fuels can be relatedto hydrogen content or content of low molecular weight constituents. Itis thus desirable to keep the molecular weight of the exhaust productsas low as possible so that higher impulses can be derived. As a resultit has been found that the boraneterminated beryllium hydride possessesa higher theoretical H content than beryllium hydride. H contentexpressed as a percentage was calculated according to the followingequation:

Hydrolyzable H (mmoles mg.) X 100 =Hydrogen Content The H content isthus a measure of hydrogen per unit mass as compared to that found inpure beryllium hydride which gives 0.1814 mmole H per milligram uponhydrolysis. As a result, the material of this invention which has EHgroups as terminators always product theoretical H contents greater than100 percent since the BH group yields more hydrogen per unit mass thandoes a BeH group. The increase in specific impulse obtained has beenshown by way of calculations from a theoretical hybrid system using H asan oxidizer. In such a system wherein the theoretical chamber pressureis 1000 p.s.i.a. and the exit pressure is 14.7 p.s.i.a., berylliumhydride has an impulse of approximately 357 seconds. Theboraneterminated beryllium hydride compound wherein n is greater thanhas an impulse of up to 359.5 seconds, for example where n equals 3540.The following specific examples disclose the preparation of thecompounds of this invention:

EXAMPLE I The reaction of alkyl aluminum compound and the berylliumborohydride of the invention was conducted in glass bulbs of 100-200mls. capacity containing magnetic stirrers and fitted with aFischer-Porter valve. A standard ball joint for attachment to a vacuumsystem was provided. The solvent utilized in the reaction and the alkylaluminum compound were loaded in a dry box. The bulbs were then attachedto a vacuum system. The beryllium borohydride was first sublimed intothe bulbs and its Weight was obtained by differential weighings on astorage container. The bulb was then immersed to the valve in a heatedoil bath. After reaching the desired temperature, the solutions formedremained clear for 1 to 4 hours before a precipitate appeared. Afterheating, the bulbs were returned to the dry box and cut open, and theprecipitated products isolated by filtration. In this example, thereaction was run utilizing essentially equal molar quantities of thealkyl aluminum compound and beryllium borohydride. Thus 18.1 mmoles oftriethylaluminum, Al(C H and 18.8 moles of su'blimed berylliumborohydride, Be(BH were utilized. The triethylaluminum was dissolved in50 mls. of benzene before the sublimed beryllium borohydride was added.The mixture was stirred at ambient temperature overnight. This wasfollowed by heating the composition from 25-60 C. for one hour and then55-60 C. for five hours. The solution remained clear at ambienttemperatures. Precipitation of the solid product began after one hour ofheating. The product isolated by filtration was 83 Weight percent pure(BeH in a yield of 230 mgs.

EXAMPLE II The procedure and apparatus of Example I was repeatedutilizing an excess of the alkyl aluminum compound. In this example 36.7mmoles of tri-n-propyl aluminum was solved in 20 mls. of normal hexaneas a solvent. Into the dissolved aluminum alkyl compound was thensublimed 30.2 mmoles of beryllium borohydride. The reaction flask washeated at 30 55 C. for two hours followed by heating from 50-55 C. forthree hours. It was observed that the solution was clear forapproximately three hours and rapidly deposited a large amount of whiteprecipitate. Analysis of the precipitate showed that it was 75 weightpercent pure (Bel-1 This precipitate was then heated to C. in vacuo forfive hours to give a final (BeH product of 97 weight percent purity.

EXAMPLE III To form the borane-terminated beryllium hydride of theinvention, the procedure of Example I was repeated utilizing 15.5 mmolesof tri-n-propyl aluminum dissolved in 40 mls. of normal hexane as asolvent. To the aluminum alkyl was added 30 mmoles of berylliumborohydride by sublimation. The mixture was heated at 26-55 C. for onehour and then continued at 5 5-5 9 C. for three hours. It was observedthat some beryllium borohydride was undissolved throughout theprocedure. Precipitation of the solid product began during the firsthour of heating. The product analysis indicated an H content of 102percent based on the equation for this determination previously given.The beryllium weight percent of the composition was 65.2, the weightpercent of the boron was 10.4. These analysis correspond to thecomposition Two hundred milligrams of the borane-terminated berylliumhydride were obtained.

EXAMPLE IV The procedure of Example III was repeated utilizing 21.6mmoles of triethylaluminum in 50 mls. of benzene as a solvent. To thealkyl aluminum was added 59.1 mmoles of beryllium borohydride bysublimation. The mixture was heated at 50-54 C. for four hours. Twohundred seventy milligrams of a borane-terminated beryllium hydride wasobtained having the composition Although the invention has beendescribed and illustrated in detail, it is to be clearly understood thatthe same is by way of illustration and example only and is not be takenby way of limitation, the spirit and scope of this invention beinglimited only by the terms of the appended claims.

5 6 We claim: Be(BH 1. The process of formlng berylllum hydridecompounds 4. (BeH2)n(BH3)2 wherein n varies from 3 to 10 according tothe reaction of Be(BH with AIRR'R" wherein, R, R and R" are selectedfrom the class consist- N f d ing of H and alkyl radicals of 1 to 8carbon atoms and 0 re erences m e wherein at least one of said Rs is analkyl group. 5 LELAND A, SEBASTIAN, Primary E a iner 2. Forming thecompounds according to claim 1 wherein said reaction occurs in thepresence of an organic US. Cl. X.R.

solvent and at a temperature of from 0-100 C. 23 363, 365; 149 22; 260448 3. The process of claim 1 wherein said AlRR'R" is 10 present in atleast an equimolar quantity to said

1. THE PROCESS OF FORMING BERYLLIUM HYDRIDE COMPOUNDS ACCORDING TO THEREACTION OF BE(BH4)2 WITH AIRR''R" WHEREIN, R, R'' AND R" ARE SELECTEDFROM THE CLASS CONSISTING OF H AND ALKYL RADICALS OF 1 TO 8 CARBON ATOMSAND WHERIN AT LEAST ONE OF SAID R''S IS AN ALKYL GROUP.
 4. (BEH2)N(BH3)2WHEREIN N VARIES FROM 3 TO 100.